Kinger isn't crazy, he's grieving
Maybe kinger isn't crazy when he's not in the darkness.
Theory 1: Maybe kinger is just grieving..and not healthily, maybe him loosing his wife, and other characters drove him to simply spiral, almost like we see caine do when he thinks the characters dislike his adventures. Maybe it's not just him grieving Queenie either maybe he it's his guilty conscious that helped drive him to "madness" it would make sense especially if you believe the theory that he helped create the circus or that he was a programmer or just a part of it in some way In general. It makes sense for him to spiral considering the only did he lose his wife but he also lost his wife do to a program he helped create, a program that also goes on to torture others as well. Maybe that has something to do with his calmness in the dark, because in one episode we find out that while Queenie is abstracting/abstracted she is calm in the dark. Maybe caine even gave kinger the idea, or simply put it in his head, to build a pillow fort for her,. somewhere in his madness deep down he remembered her calmness in the dark and that's how he figured the dark also calmed him. At one point it's believed he reached to touch abstracted Queenie in her last moments before caine sent her off..maybe that's why he has some characteristics such as the calmness in the dark but the craziness in the light.